Slow-Flow Malformations

What Are Slow-Flow Malformations?

Slow-flow malformations are abnormally formed veins or lymphatic channels (channels that run parallel to veins, and are part of the immune system), that can happen anywhere in the body (excluding the brain). Rather than maintaining the normal appearance of a “tube” or “pipe”, these malformations appear like expanded complex “lakes” of blood, lymph fluid or both. There are three kinds of slow-flow malformations:

  1. Venous Malformations – The veins in a venous malformation are formed irregularly before birth and become enlarged. They can occur anywhere on the body (except the central nervous system), from head to toe and may be seen in skin, mucosa (the lining of body cavities), subcutaneous tissue, muscle and rarely bone. This is the most common vascular malformation. 
  2. Lymphatic Malformations – These are masses that result from an abnormal formation of small tube-like vessels that collect and transfer fluid in the body's tissue and are part of the immune system. In the normal lymphatic system, extra fluid is collected from the tissues and transported through a series of these vessels back into the body’s veins. With a lymphatic malformation, however, transfer of this fluid through these vessels is slowed down. The extra fluid builds up and dilates the vessels, which causes the affected area to swell, and sometimes, soft tissues and bones to enlarge.
  3. Mixed (Veno-lymphatic) malformations – This occurs when the combination of the two types of bone makes up the malformation.

What Causes Slow-Flow Malformations?

Slow-flow malformations are a congenital condition. In most cases no clear cause is found. In a minority of cases they are due to certain genetic conditions such as Klippel Trenaunay syndrome, blue rubber bleb nevus syndrome, multiple cutaneous and mucosal venous malformations, and glomovenous malformations.

What Are the Signs & Symptoms of Slow-Flow Malformations?

The signs and symptoms of slow-flow malformations depend on several factors including size of the lesion, location of the lesion in the body, type of malformation, and the patient’s age or condition.

In general, the larger the lesion, the more likely it is to be noticed earlier. Lesions that are superficial, and/or involve the face/neck/extremities are more likely to be noticed earlier. Lesions that affect functional organs of the body, such as the tongue, eye socket, eyelids or extremities can cause functional problems and are often diagnosed earlier.

These malformations can grow with puberty or pregnancy and can therefore come to attention during those episodes.

How Are Slow-Flow Malformations Diagnosed?

The visual appearance of the lesion (color, response to pressing on the lesion) and the behavior of the lesion are often accurate in predicting the type of malformation.

For example, venous malformations are often bluish in color (if close to the skin or mucosa of the mouth/nose) and will swell with certain maneuvers such as straining or crying (in children). Lymphatic malformations in the head and neck can enlarge during upper respiratory infections.

Imaging studies are the mainstay of diagnosis and help in both knowing what kind of malformation the individual has and the size and extent of the malformation. The modalities used include ultrasound, CT and MRI scanning. MRI is overall the most helpful imaging technique.

How Are Slow-Flow Malformations Treated?

The available treatment methods include:

  • Minimally-invasive, image-guided sclerotherapy
  • Surgical removal
  • Surgical removal following image guided embolization (filling) of the malformation
  • Medical therapy

Since many slow-flow malformations cross the border of different tissues (for example extending from muscle into the adjacent fat) or can involve functional organs (such as the tongue), surgical resection is often difficult and sometimes ineffective.

The mainstay of treatment for most small and medium sized malformations is image-guided, minimally invasive “sclerotherapy” or “embolization” using needles that are advanced into the malformation, allowing injection of special medications to cause scarring and shrinkage of the malformation. Depending on the size of the lesion and its response, several treatments may be necessary.
Very large lesions are difficult to treat with sclerotherapy or embolization but can respond favorably to certain medications administered by an experienced oncologist.

At Lurie Children's, patients are seen in a multi-disciplinary clinic which includes experts from all the relevant specialties, who design a consensus-based treatment regimen specific to each patient. 

Illustrative pictures from a percutaneous image guided treatment of a venous malformation of the forehead:

Ultrasound image showing the plastic "needle" (arrowheads) placed in the venous malformation (outlined by stars).

Image obtained in the same patient during fluoroscopy (x-ray) guided injection of contrast to ensure that the entirety of the malformation is being filled by the contrast and therefore the sclerosant that will be injected to treat the malformation. Two plastic needles are seen (arrowheads). Contrast is seen as the darker material filling the malformation (stars).

What Are the Long-term Effects of Slow-Flow Malformations?

The long-term effects depend on the size/location of the malformation and the response to treatment.

While there are many options for managing symptoms, slow-flow malformations can occasionally recur even after successful treatment. For this reason, it’s important to schedule regular follow-up visits with a specialist to minimize recurrent symptoms and associated complications.

Make an Appointment

To make an appointment with one of our Neurointerventional Radiology specialists, call 312.227.5110 or email